It is known that sources of electromagnetic radiation provide non-constant output intensity vs. wavelength characteristics. Further, it is known that detectors of electromagnetic radiation become saturated when too high an intensity is input thereto. Where the intensity of one or more a wavelengths in a spectrum of wavelengths is high enough to saturate a detector, one approach is to attenuate the intensity of all wavelengths. This can be accomplished by a Neutral density filter. Neutral density filters, however, do not pass UV wavelengths and problems can develop using this approach in that reducing the intensity of the highest intensity wavelengths causes reduction of the intensity of other wavelengths below that which a detector can detect. It is also known to cause a beam to reflect off, for instance, a silicon substrate with an oxide on its surface, to provide emphasized IR and UV wavelength intensities with respect to Visible wavelengths, but across the board attenuation is typically not realized by this approach. Another approach to generally reducing intensity is to pass a beam of electromagnetic radiation through an iris which can be reduced, in opening size, however, cross-sectional non-uniformity in the beam can lead to non-uniform results when this approach is used because of varying placement of the iris in the beam.
It is also disclosed that ellipsometers and polarimeters and the like typically comprise a source of a beam of electromagnetic radiation, a beam polarizer, a beam analyzer and a detector arranged so that a beam provided by the source passes through the polarizer, impinges on a sample and the passes through the analyzer and into the detector. The beam polarizer sets a polarization state in said beam which is changed by interaction with a sample, and the analyzer selects polarization states which are passed to the detector for analysis.
As the present invention finds non-limiting application in the investigation of non-specular depolarizing samples, it is noted that non-specular refers to reflections which are not “mirror-like”, and depolarizing samples are characterized by a depolarization parameter defined by 1.0 minus the square root of the sum of the squares of:% DEP=1−√{square root over (N2+C2+S2)}where:                N=Cos (2 ψ);        C=Sin (2 ψ) cos (Δ); and        S=Sin (2 ψ) sin (Δ).and ψ and Δ are defined by the well known ellipsometry beam orthogonal component ratio equation:        
            r      p              r      s        =      ρ    =          tan      ⁢                          ⁢              Ψ        ·                  exp          ⁡                      (                          ⅈ              ·              Δ                        )                              
As the system of the present invention includes “crossed-polarizers”, U.S. Patents and Published Applications were identified which include the terms “crossed-polarizer” and “ellipsometry” or “ellipsometer”, and are:
Patents:
7,236,221;7,221,420;7,211,304;7,163,724;7,083,835;7,061,561;6,934,024;6,798,511;6,693,711;6,112,114;5,787,890;5,303,709;4,097,110;7,170,574;Published Applications:
2006/0215158;2006/0203164;2006/0193975;2005/0286001;2005/0270459;2005/0270458;2005/0024561;2004/0189992;2004/0179158;2003/0227623;2003/0227623;2002/0091323;2006/0141466;2006/0115640;2006/0099135;2005/0270458;2005/0128391;2004/0208350;2004/0189992;2003/0227623;2002/0091323.
It is believed that the foregoing identified prior art is the most relevant to be found and has as its major thrust the application of conventional ellipsometry to the measurement of various parameters such as are common to samples which demonstrate, for instance, low specular reflectance and/or which are depolarizing, (eg. solar cells). Even in view of the prior art, however, need remains for improved systems and improved methodology which better enable application of ellipsometry to the investigation of sample characterizing parameters of samples which, for instance, demonstrate low specular reflectance and/or which are depolarizing.